It is well-known that hydrogen is a very high energy density element and clean-burning fuel. Hydrogen can be combined with oxygen through combustion, or through a fuel cell mediated oxidation/reduction reactions, to produce heat, or electrical power. The primary product of this reaction is water, which is non-polluting and can be recycled to regenerate hydrogen and oxygen.
Currently, hydrogen energetics is the focus of interest in nuclear industry, motor transport, auto industry, chemical industry, aerospace industry, etc. In particular, the transport sector is a consumer of about half of the world's crude oil production. Moreover, in large metropolitan agglomerations worldwide, road traffic represents one of the most important and fastest growing emission sources for both pollutants and noise. Hydrogen as a new vehicle fuel provides the opportunity for both the reduction or avoidance of polluting emissions, and the drastic reduction of the noise level produced.
One of the hurdles facing hydrogen energetics is safe storage and delivery of hydrogen fuel to a combustion cell. Most generally, several approaches were developed, including physical storage (liquid or compressed hydrogen) and chemical storage (hydrogen absorption in metal hydrides, and hydrogen adsorption in carbon nano-fibers). All these approaches have fundamental limitations in weight and volume capacities of the storage media.
It is known that compressed hydrogen can be safely stored in microcapsules, such as hollow glass microspherical and/or microcylindrical (multi-capillary) arrays. If heated, the glass permeability to hydrogen will increase. Hydrogen can diffuse into the hollow cores of the microspheres and/or microcylinders through the thin glass walls at a rate strongly depending upon the wall temperature. This provides the ability to fill the microcapsules with gas by placing the microspheres and/or microcylinders in high-temperature and high pressure environments. Once cooled, the microcapsules lock the hydrogen inside since the diffusion rate is drastically lower at room temperature. A subsequent increase in temperature will increase the diffusion rate. Thus, the hydrogen trapped in the microspheres can be released by subsequently increasing the temperature.
For example, U.S. Pat. No. 4,328,768 describes a fuel storage and delivery system wherein hollow microspheres filled with hydrogen gas are stored in a fuel storage chamber at pressures of 400 atm. From the fuel storage chamber the microspheres are directed through a heated delivery chamber wherein hydrogen gas is freed by diffusion and delivered to an engine, after which the substantially emptied microspheres are delivered to a second storage chamber. The substantially emptied microspheres are removed by mechanical means, such as a pump, to a storage chamber from which they can be removed for refilling.
International Publication No. WO2006/046248A1 to Chabak describes a hydrogen accumulation and storage material and a method of forming thereof. The material comprises a plurality of various-sized and at least partially permeable to hydrogen microspheres bound together to form a rigid structure in which a diameter of the microspheres is reduced from a center of the structure towards edges of the structure. An outer surface of the rigid structure can be enveloped by a sealing layer, thereby closing interspherical spaces.
International Publication No. WO2005/028945A2 to Vik describes a storage apparatus for storing a highly pressurised gas such as hydrogen. The apparatus comprises an outer vessel and a plurality of separately sealed inner vessels. Means are provided for communication with the interiors of the inner vessels and of the outer vessel respectively. The inner and outer vessels may be of any suitable shape. For example, the inner vessels are substantially spherical. Alternatively, the inner vessels are in the form of tubes which are preferably straight and parallel to one another. The inner vessels are preferably made of carbon fibre reinforced epoxy.
International Publication No. WO2007/072470A1 to Gnedenko, et al. describes an apparatus for storage of compressed hydrogen gas. The apparatus includes a sealed housing that defines a chamber that includes a cartridge comprising a plurality of cylindrical voids containing the compressed hydrogen gas. The apparatus also includes a hydrogen liberating tool configured for controllable liberating the hydrogen gas from the cartridge into a volume of the chamber that is not occupied by the cartridge.
According to one embodiment described in WO2007/072470, the cartridge includes an assembly structure formed of a plurality of closely packed hollow microcylinders having sealed ends. In this case, the hydrogen liberating tool can include an electrically heating element, such as a wire woven within the cartridge in empty inter-cylinder spaces along the microcylinders, for liberating the hydrogen stored within the microcylinders into the inter-cylinder spaces and the other volume of the case that is not occupied by the microcylinders. Alternatively, the liberating tool can include a mechanical opener that is mounted on a shaft of an electric drive and configured for gradual destroying of the microcylinder ends proximal to the liberating tool.
According to another embodiment described in WO2007/072470, the cartridge includes a monolithic block having a plurality of cylindrical cavities. The ends of the cavities, proximate to the hydrogen liberating tool, are covered with a hydrogen diffuser plate. In this case, the hydrogen liberating tool includes a controllable radiation source for providing photo-enhanced diffusion of hydrogen through the hydrogen diffuser plate.